A camera may have an axis offset between an optical axis of an image pick-up optical system as a first optical system for focusing an image on a photoelectric detector with a focusing lens and an optical axis of a second optical system for displaying the image in a view finder an operator looks into. This camera cannot avoid parallax. Unless the object is located at a point called a crossover point COP, there is a positional deviation between the image seen through the view finder and the image actually picked up as shown in FIG. 5A. For example, assuming that an operator attempts to pick up the image of an object X in front of the crossover point COP as shown in FIG. 5B. When the object X is captured at the center of the view finder as shown in FIG. 6A, the object X positions offset to the right on the image screen as shown in FIG. 6B. On the other hand, in case of imaging an object Y far behind the crossover point COP as shown in FIG. 5C, the object Y positions offset to the left as shown in FIG. 7B when the object Y is captured at the center of the view finder as shown in FIG. 7A.
With a camera with parallax, even if an operator attempts to focus an object by capturing the object at the center of a view finder, the parallax causes the object to move out of a focus evaluation area at the center of the image screen formed through the image pick-up optical system, making it impossible to focus the object.
A prior art camera employs an evaluation window, which is capable of moving in a screen formed in a view finder in response to variation of the object distance, in order to avoid parallax. The evaluation window defines the window for an object to be focused. However, an automatic focusing camera with a zoom lens requires the movement of such window or evaluation window on the basis of the variation in not only object distance but also focal length or zoom magnification. This leads to a complicated mechanism for evaluation window movement.
For simplicity the mechanism may employ two stationary evaluation windows for an infinite imaging and a nearest imaging with the largest zoom magnification in an image screen formed in a view finder. However, with this facilitated method, an operator cannot determine the center position of the image screen at various zoom magnification and object distances. Attempts by an operator to focus thereby lead to blurred images.